The invention relates to a process and a device for rapid profiling of topologically corrected grinding worms as they are used for continuous generating grinding of gear teeth.
Topologically corrected gear teeth on highly loaded gear wheels are increasingly used in transmission gears that have to run at an especially low noise level. Wheels corrected in such a manner are needed in increasing numbers, particularly in motor vehicles but also in the aircraft industry.
Corrected tooth flanks may be manufactured most efficiently and with high precision in the continuous generating grinding process by continuous shifting of the grinding tool during the work process. There is a problem, however, in that the manufacturing of the necessary tools, specifically the grinding worm profile, take possibly a lot of time. This is caused because in general technology this grinding worm profile can be manufactured only with a tool that comes into contact with the worm flanks only at a single point.
The topological generating grinding process with continuous shifting is based on the fact that during grinding of the gear work piece there is for each point of the tooth flank surface a precisely predetermined individual matching point on the grinding worm profile whereby this matching point on the flank is ground during the grinding process and thereby shaped to the required specification. In other words, the desired geometric shape of the topologically corrected tooth flank surface is included in transformed manner on the grinding worm flank surfaces and appears again in a transformed manner during the grinding process on the tooth flank because of the relative motion between the grinding worm and the work piece. During profiling of the grinding worm there is therefore the challenge to create the required tooth flank topology on the worm flank in a transformed manner.
Computer programs have been developed to determine this transformed topology, which requires the geometric shape of the specific tooth flanks as entry data, for example in form of a table that contains deviation values of the theoretically exact tooth flank area in relation to specifically defined points on the tooth flank surface. As a result, these programs provide again a table that specifies the coordinates of points of the specific geometry of the worm flanks. These calculating programs additionally require different processing data like the ratio of grinding path to shifting path or the amount of modification caused by the infeed of the tool etc. After creation of such a table with specific data of the worm flank geometry, the production of a grinding worm may be principally compared with the production of any kind of free-formed surfaces, as for example die blocks for forging sheet metal for automobiles. In both cases, corrections to specified shapes are only possible with the use of tools that machine with point contact. In case of die blocks there is a die-sinking cutter necessary; in case of worm shaping there is necessary a correspondingly designed rotating diamond cutter. Whereas there are normally at least three linear N/C axes necessary in case of a die-sinking cutter, there are usually two linear axes in the topological profiling of grinding worms for the movement of the rotational diamond cutter an one rotating N/C axis for the turning motion of the grinding worm.
As mentioned above, the processing of a free-form surface or the profiling of topological grinding worm flanks take a very long time since the entire surface must be covered with a tool line by line to bring each individual point to its final specification.
It is the object of the present invention to show a procedure and a device, as well as a profiling tool, with which the topological profiling of grinding worms is performed more rapidly. This object is achieved by the combination of characteristics in the claims.
The basic idea isxe2x80x94within a certain limitsxe2x80x94that the reproduction and transfer of a free-form surface to another in a transformed manner is possible and also in reverse. Should therefore a work piece have teeth that have the desired topology and should the grinding worm flanks be profiled with said teeth then reproduction in the reverse direction as above would occur during a process, which could be the same as the grinding process. The grinding worm would thereby be profiled in a very short time. Also an initial gear with a very large face width, which would have to have the specified topology in a correspondingly stretched manner, would be suitable for fast profiling at appropriate ratio of grinding stroke and shifting path.
Should there be therefore a working face, which makes possible a definable arrangement of matching points on the to-be-manufactured surface during reproduction and should this working face be produced in its transformed shape and be covered with a suitable abrasive surface coating, for example with fine diamond grit, then the production of a topological surface is thereby made possible in a very short time span. Working faces are preferably used that have a simple geometric basic shape and which may be manufactured in a simple way. For example, the above-mentioned toothed wheel, which would be principally well suited for profiling, is difficult to be manufactured with high precision. In contrast, items with essentially flat surfaces or profile discs would be much more suitable.
In the simplest version of the invention, a straight rod is used for the profiling shaping of a topological grinding worm profile. The rod has a cross section that matches the worm groove, which has an abrasive surface that is, for example, coated with hard-material grains. This rod is placed for profiling against the worm groove in such a manner that one part of its cross section comes into full contact with the groove. Should the rod now be brought into contact further with the worm profile itself so that each longitudinal position of the rod matches a certain place on the worm path, then the above-mentioned requirement is fulfilled and the transformed shape of the rod surface may be transferred onto the worm flank.
During the rotation of the grinding worm there is not only necessary the movement of the rod in axial direction of the grinding worm (depending on the worm pitch) but at the same time a longitudinal shifting of the rod is necessary in the direction of the rod axis in order to always keep a new cross section in contact with the worm flank.